Currently, a high-order modulation format using a higher baud rate is a preferred solution to further increase an interface rate of a single fiber. However, the high-order modulation format using the high baud rate is very sensitive to IQ (in-phase and quadrature) imbalances and inter-path crosstalk of an optical transmitter and receiver. The IQ imbalances mainly include the following effects: an amplitude imbalance between an I-path and a Q-path, a phase imbalance between the I-path and the Q-path, an amplitude-frequency response and phase-frequency response imbalance between the I-path and the Q-path, and a delay skew between the I-path and the Q-path. In addition, since the optical transmitter and receiver have a plurality of paths of input and output, crosstalk between the plurality of paths due to circuit wiring and the like also causes a certain performance penalty. It can be seen that in an optical communications system, impairments of the transmitter end and receiver end mainly include: an IQ amplitude imbalance, an IQ phase imbalance, an IQ amplitude-frequency response and phase-frequency response imbalance and IQ delay skew and crosstalk between a plurality of paths.
In order to detect and compensate for these impairments, a number of different methods have been proposed. Common to these methods are that filter coefficients used for compensating for the impairments are iterated and updated by a filter in a real-time manner, and the impairments are compensated for in a real-time manner.
It should be noted that the above description of the background is merely provided for clear and complete explanation of this disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of this disclosure.